1. Field of the Invention
The present invention relates to a multilayer electronic device and a method for manufacturing the same, and more particularly to a multilayer electronic device formed by plating external electrodes directly on external surfaces of a laminate and to a method for manufacturing the multilayer electronic device.
2. Description of the Related Art
As shown in FIG. 6, a multilayer electronic device 101, which is represented by a multilayer ceramic capacitor, includes a laminate 105 including a plurality of insulating layers 102 laminated to each other and a plurality of layer-shaped internal electrodes 103 and 104 provided along interfaces between the insulating layers 102. At one end surface 106 and the other end surface 107 of the laminate 105, edges of the internal electrodes 103 and edges of the internal electrodes 104 are exposed, respectively, and external electrodes 108 and 109 are arranged to electrically connect the edges of the internal electrodes 103 and the edges of the internal electrodes 104, respectively.
When the external electrodes 108 and 109 are formed, in general, paste electrode films 110 are first formed by applying a metal paste including a metal component and a glass component on the end surfaces 106 and 107 of the laminate 105, followed by firing. Next, on the paste electrode films 110, first plating layers 111 including Ni or other suitable material as a primary component are formed, and furthermore, on the first plating films, second plating films 112 including Sn or other suitable material as a primary component are formed. That is, each of the external electrodes 108 and 109 have a three-layer structure including the paste electrode film 110, the first plating film 111, and the second plating film 112.
The external electrodes 108 and 109 must have superior wettability to solder when the multilayer electronic device 101 is mounted on a substrate using solder. At the same time, the external electrode 108 electrically connects the internal electrodes 103 which are in an electrically insulated state, and the external electrode 109 electrically connects the internal electrodes 104 which are in an electrically insulated state. The second plating film 112 ensures the solder wettability, and the paste electrode films 110 electrically connect the respective internal electrodes 103 and 104. The first plating film 111 prevents solder leaching during solder bonding.
However, the paste electrode film 110 has a relatively large thickness, such as several tens to several hundreds of micrometers. Thus, when the dimensions of this multilayer electronic device 101 are set within a predetermined standard value, an effective volume to ensure an electrostatic capacity is decreased by an amount corresponding to the volume of the paste electrodes 110. On the other hand, since the thickness of each of the plating films 111 and 112 is approximately several micrometers, if each of the external electrodes 108 and 109 can be formed only by the first plating film 111 and the second plating film 112, a larger effective volume for the electrostatic capacity can be provided.
As described above, when the external electrodes are directly formed on the end surfaces of the laminate by plating, it is necessary not only to deposit plating deposits on edges of the internal electrodes exposed at the end surfaces of the laminate but also to grow the plating deposits so as to be mutually cross-linked to each other. However, as the distance between the edges of adjacent internal electrodes is increased, even if plating growth occurs, the cross-linking is not likely to occur. In this case, connection failures between the internal electrodes and the plating films and degradation in the insulating resistance due to intrusion of moisture and other contaminants may disadvantageously occur.
In addition, it is virtually impossible to form the external electrode on not only the end surface of the laminate but also to extend on portions of side surfaces adjacent to the end surface. The reason for this is that the edges of the internal electrodes are not exposed at the side surfaces of the laminate.
A technique for solving the above-described problem, for example, is disclosed in Japanese Unexamined Patent Application Publication No. 2004-40084. Japanese Unexamined Patent Application Publication No. 2004-40084 discloses that in a region in which an external electrode is to be formed, edges of dummy electrodes are exposed at locations at which edges of internal electrodes are not exposed. With this technique, even in a region in which exposed edges of the internal electrode are not provided or a region in which the distribution density thereof is low, plating deposits are likely to be cross-linked to each other, and thus, by plating, a reliable external electrode can be formed. In addition, when the technique disclosed in Japanese Unexamined Patent Application Publication No. 2004-40084 is used, even on the side surfaces at which the edges of the internal electrodes are not exposed, the external electrode can be formed by plating.
However, when the technique disclosed in Japanese Unexamined Patent Application Publication No. 2004-40084 is performed, since internal electrodes defining the dummy electrodes are required, in addition to the actual internal electrodes, the total number of the internal electrodes to be formed is increased. Thus, a step of forming the internal electrodes is complicated, and as a result, the manufacturing cost is increased. In addition, when the locations at which the dummy electrodes are to be formed, or when the dummy electrodes are displaced when being laminated to each other to form a laminate, the dummy electrodes may not be appropriately exposed at predetermined locations. When the dummy electrodes are not sufficiently exposed, a plating film may not be uniformly formed. When the plating film is not uniformly formed, connection failures with the actual internal electrodes may occur, and as a result, the reliability of a multilayer electronic device may be decreased.